Fuse for electric circuits



Aug. 22, 1933. A, APPEL 1,924,014 j FUSE FOR ELECTRIC CIRCUITS Filed s t. 14, 1951 5;; mummy fl 5!, .1

C I W Patented Aug. 22, 1933 I UNITED STATES 'PATENT OFFICE FUSE FOR. ELECTRIC cmom'rs August Appel, Vienna, Austria Application September 14, 1931, Serial No. 562,771, and in Austria September 19, 1930 Claims.

This invention relates to fuses of the type in which a switch member, on the attainment or overstepping of a certain temperature limit, performs a switching or. cutting out action. Fuses 5 of this type are generally equipped with a switch 1 the drawback that often mere softening ofthe solder and partial cutting out of the current supply take place, thus giving rise to the lo se contacts which are so troublesome and generally so diflicult to trace in such systems. After repeated use the solder also becomes easily altered as to its composition. and therefore also in its melting point, so that there are considerable variations in the temperature and time reposed to be identical. Moreover the, quantity of solder applied varies, and exercises an indeterminate'influence on the actual time required for melting the same. Further, in the case of 3 interiorly situated and inaccessible fuses it is practically impossible to check the quality of the soldering work, so that it not infrequently happens that such fuses become loosened or broken by mere vibration or concussion.

' Thermically operated switches for the protec tection of .machines and apparatus from overheating are also alreadyknown, in which a slotted plate of a readily fusible metal retains under tension a switching rod which controls a current 40 circuit; In switches of this type the'rod or other switching member proper must first be tensioned and held in position, after which a slotted plate or fork-shaped piece of the fuse metal is inserted between a specially shaped head on the said bar or member and a fixed portion of the switch. The insertion of new fuse elements thus requires a number of operations and the use of elements specially made to suit the shape of the switch members. These circumstances become a source of very considerable inconvenience and loss of time when a large number of fuses are replaced as in the case of automatic telephone systems. The present invention obviates the above-mentioned drawbacks, and provides a non-soldered fuse responsive to excess current and excess voltage in which a switch member heated by the current is held in tension by a plate of the fuse metal, and is adapted to interrupt the current circuit by a movement relative to a second switch member on the attainment or overstepping of a certain maximum strength of current. In accordance with the invention, the fuse consists of, two detachably connected parts of which the one contains the spring-tensioned switchmemher, and the other providesthe counter support therefor and receives the loosely inserted fuse plate, so that by the mere bringing together of these two parts the movable switch member is tensioned and the fuse plate positioned between j I the two members as required. Thus to remove the used fuse plate it is merely necessary to disconnect the two parts, and after the insertion of a fresh fuse plate it is merely'necessary to bring the two ,parts together again in order to put the fuse into working order. In the simplest form of construction the movable switch member takes the form of a pin subjected to spring action andadapted to be by. a heating coil traversed quired for melting between fuses which are supby the checked In order pre;

vent thefuse metal when melted from dropping and-lodging in the adjacent mechanism the invention is further developed to comprise a modifled form of fuse in which, instead of the movable pin being heated, th'eheating coil is applied to a tubular member which forms the counter sup port for the plate of fuse metal. The pin as before is pressed by a spring. against the middle of the fuse plate. But in this case the fuse plate is heated annularly by'the supporting end of the saidtubular member, so that when the fuse metal has become sufiiciently softenedthe shearing strain between the outer edge of the end of v the switch rod or pin and'the inner edge of the supporting end of the tubular member coupled with .the force of the spring causes the middle of the fuse plate to be punched out, thus liberating the pin to move in response to the spring. Since in this case no actual melting of the fuse metal takes place no clogging orunintentional soldertion, a form of construction in which the switch pin is heated, and Fig. 2, likewise in section, a

form in which a tubular counter supporting.

member for the fuse plate is heated. 7

Referring to Fig. 1, a cartridge-shaped metal case 1 is traversed axially by a metal pin 2, these two parts being insulated from each other by means of a bush or plug 3 of insulating material inserted in the case. The pin 2, which may consist of drawn copper wire, has attached to it a disc 4 of insulating material which can slide with an easy fit in the case 1. A helical spring 5 is inserted and adapted to be compressed between this disc 4 and the plug 3. The pin 2 is further fitted with a plate of insulating material 6 which is provided with a metallic ring? of good con ducting material. Between the two discs 4 and 6 thereis 'woundupon the pin 2 the heating coil 8 of resistance wire the one end of .which is connected to the pin 2 and the otherv end to the ring 7. A cap 10 having acentral hole is adapted to be fitted over the open end of the case 1, and to be attached thereto by means of a bayonet joint or in any other mannerpermitting of ready disconnection. Into this cap 10 there is inserted an insulation ring 11 with a conically tapered or shouldered rim for the reception and centralizetion of the fuse plate 12. This plate is held in position by the end of the pin 2-.which is pressed firmly'thereon bythe spring 5. The complete fuse is interposed in the current circuit by means of thespring and of a metal ring 13 with a projecting tongue 14 inserted between the end of the case 1 and the plug 3. 16 denotes a contact spring with which, after the melting of the fuse plate 12, the pin 2 comes into contact, as indicated lows:The' current flowing through the fuse passes from the spring 15 through the copper pin 2 into the heating'coil 8 consisting of wound resistance wire and thence to the ring 7. From this ring the .current' passes through the tongues 9 into the casing 1 whichis connected through the metal ring 13 and tongue 14 to the supply line. When the current in the fused circuit increases beyond a certain permissible limit the copper pin 2 is heated'by the heating coil to such an extent that the pin can perforate the fuse plate 12, and is ejected by the spring; through the hole in the head of the cap 10 to form contact with the earthed contact springl8, as'indicate'd in dotted lines in'the drawing. This movement of the pin renders the heating coil 8 dead and in- The open end is covered by a metal cap 18 which is bayonet-jointed or otherwise detachably conto the diameter of the pin 20, so that this pin can pass therethrough under thethrusting action of the spring 23. I The outer edge of the end of the pin 20 and the inner edge of the end of the tube 27 are adapted to cooperate with a shearing action, in the manner of a die punch. The one flange is cupped to receive the fuse plate 28.

Y The tube 27 is fitted with the heating coil 29 the on'eend of the wire of which is connected to the ,tube 27, while the other end is connected to the cap 18 and therefore also with the sleeve 1'7. The

. cap 18 is provided with a hood-like extension 30 with an opening 31 for the reception and removal of the punched-out portions of the fuse plates. A projection 32 on the sleeve 17 serves for the attachment of the fuse to its holder.

As will be seen from the drawing (Fig. 2), the current to be limited passes through a contact spring (not shown) into the pin 20 the one end of which projects sufliciently far from the end of the sleeve in consequence of the fact that the other end of the same is retracted against the action of the spring 23 and rests against the fuse plate. 28 supported by the end-of the tube 27. The current then travels through the pin, fuse plate, tube 2'1, heating coil 29, and into the cap 18 and sleeve 17.

The heating of the tube 2'7 causes the fuse plate pressed against the end thereof, when the current reaches a certain limit, to be softened to such an extent that the force of the spring 23 causes the middle of the fuse plate to be punched out and thrust by the movement of the pin 20 into the hood 30 from which it can be removed through the opening 31. The presence of this hood prevents the punched-out portions of the fuse plates from becoming lost or from causing short-circuiting or other derangement in the apparatus in which the fuse is used. The forward movement of the pin 20 under the action of the spring 115 23 interrupts the current circuit by bringing the end of the pin out of contact with the lead-in contact spring. As already mentioned, with this form of fuse the fuse plate is perforated without being melted, so that there is no danger of clog- 1 20 ging or of soldering together parts offlthe adjoining mechanism, and the fuse is reset for operatisnnlliiythe simple insertion of anew plate.

1. In a fuse in electric current circuits of the 12s type in whichv a switch member heated by the current is caused to. execute a switching action by I I switch-member in the one of the said 18.6 spring adapted to press the saidmember inj axial direction, thesecond of the saidntwofparts adapted to serve as a counter supportto the said member, and a plate-of easily fusible metal looseanew" ly inserted in the said second part, "the said 159 :1 and the said member being so'dimensioned-thst I nected to the sleeve 17. Within the "sleeve 17 and insulated therefrom there is slidably mounted a pin 20 which is guidedby two discs 21 and 22 of insulating material in the sleeve 17. A helical spring 23' which'bears with its one end against the insulation disc 21 and with its other end against a collar 24 on the pin'20 tends to press the pin 20 against the cap 18. In the cap 18 there is mounted. by means the said-plate is brought, into position between the said memberand the said second part of the casing and the said member is put-under tension-f against the action of the said springby the-mere .145

action of bringing the two said parts together? a 2. In a fuse as claimed in. claim 1, the said-two parts consisting of a sleeve and a cam-respectively.

of flanges 25 and 28 of insulating material interconnected by'means of ajointadapted tobe' a small metal tube 27 the bore of which is equal I readily taken. apart and reasscmbledby hand without the use or tools, the said am consisting of a pin, and a heating coil consisting of resistance wire being interposed in the current circult and would about the said pin.-

3. Inatuseasclaimedinclaim 1, andof the type comprising a tubular member and a heating coil wound about the said tubular member, the said member being adapted to serve as a countersupport for the loosely inserted plate 0! readily fusible metal, and being open at both ends. for the p se of enabling a stamped-out portion of the said plate to pass unhindered through and out 0!- the said tubular member.

4.Inai.'useasclaimedinclaiml,thesaid movable switch member being a pin slidably mounted within and insulated from the said first member the said car? being adapted to establish electric connection between the one end 015 the said heating coil and the said casing.

5. In a fuse as claimed in claim 1 a hood-shaped extension on the said second part of the casing for the reception of the detached portion of the plate of easily fusible metal.

' AUGUST APPEL. 

